Fire is the deadliest in France since 2005, when a Paris apartment building fire killed 18 people.

French bar birthday celebrations results in 13 killed in a fireReuters

A deadly blaze at a birthday celebration may have been caused by a woman who tripped while carrying a cake into the basement. The walls and ceiling quickly caught on fire when the lit candles of the cake fell on the floor, according to local media. There were claims that the walls and low ceiling had a sound-proofing layer of foam padding, and this inflammable material caused the fire to spread throughout the building.

Bernard Cazeneuve, French interior minister, gave an initial death toll of 13 dead and six injured. The inferno is believed to have started in the basement of the Cuba Libre bar in Rouen, Normandy. The dead are aged between 18-25, with some of them overcome by toxic fumes. More than 50 firefighters were called to the scene to fight the fire at around 1am on Saturday (6 August), which is not believed to be an act of terrorism.

Yvon Robert, Mayor of Rouen, said it was "the greatest catastrophe" that had befallen Rouen, she told Paris Normandie.

"It's an ordinary birthday party that ended tragically," she said. The bodies were taken to the University Hospital but they have yet to be identified. A criminal investigation is underway to find out the cause of the fire.

"Police sources being quoted by the local media are suggesting, quite extraordinarily, that one of the partygoers was carrying a birthday cake down the stairs from the ground floor into the basement," said a Sky News correspondent. "The birthday cake obviously with candles on it.

The reports suggest that she tripped, the cake fell onto the ground, and somehow the foam padding caught alight very quickly, it is suggested, and that is what caused such a quick and fierce fire to take hold."

One of the injured suffered burns to nearly 90% of their body and was in a critical condition, a police official added.

"All of a sudden, everything blew," said Valerie Fouquet, who was outside at the time of the fire.

"We saw the smoke and we saw the flames, the chairs flew up, the window exploded."

Prime Minister Manuel Valls tweeted (in French): "Deep sadness with regard to the tragedy which mowed down 13 young lives. Compassion and support for the afflicted families."